Jan. 23, 2012 -- A drug widely prescribed to treat men with enlarged prostates may also slow the growth of early prostate cancers, according to a new study.

Researchers say the drug Avodart (dutasteride) may reduce the need for aggressive treatments in men who have a very low risk of dying from their disease.

But there are also concerns that the drug and others in the same class may have no effect on more deadly cancers or may actually fuel their growth, leading several experts to conclude that more study is needed before they can be recommended as a treatment of prostate cancer.

"These drugs are not without side effects," says Durado Brooks, MD, MPH, who is director of prostate and colorectal cancers for the American Cancer Society. "They do seem to decrease the growth of low-grade cancers, but questions remain about whether they have much activity against high-grade disease."

Most Prostate Cancers Aren't Deadly

As many as 1 in 5 men in the United States will be diagnosed with prostate cancer at some time in their lives, but most have low-risk cancers that will never cause them harm.

Withholding treatment while closely monitoring the cancer, known as watchful waiting or active surveillance, is increasingly recommended as an alternative to surgery or radiation for men with low-risk cancers.

The strategy is now common in many parts of the world, but most American men still opt for active treatment.

"Nine out of 10 men with low-risk disease in the U.S. are still getting treatment, either because they aren't offered active surveillance or because they rejected it," Brooks says. "Americans are action oriented, and the idea of not treating a known cancer goes against the U.S. psyche."

Since surgery and radiation involve a risk of life-altering side effects, including erectile dysfunction and incontinence, different treatment approaches are needed for men with low-risk disease, says Neil E. Fleshner, MD, MPH, of Toronto's Princess Margaret Hospital.

Fleshner and colleagues recruited slightly more than 300 men with low-risk prostate cancers to assess the impact of Avodart on cancer progression.

Avodart-Treated Patients Less Anxious

Roughly half the men in the study took the prostate drug for three years while the other half took placebo pills.

Biopsies were performed after 18 months and three years to measure disease progression, and the men completed questionnaires about how anxious they were about their cancer.

Men treated with Avodart reported significantly less cancer-related anxiety.

They were also more likely to have delayed prostate cancer progression and show no evidence of cancer on their final biopsy.